Michael Symon's Apple and Celery Root Salad

This is one of those recipes that surprised me.  It sounded pretty good, and Michael Symon recommended it with pork, so when I made some porchetta, I decided to have this on the side.  I found it in Michael Symon's Carnivore cookbook.  It is such a great complement to rich ham/pork, and very easy to put together.  I bet it would be even easier if one had a mandolin, which I don't, because the most time-consuming part was the chopping.  This made eight servings, and each serving was 161 calories.  This also still tasted great the next day, so we could have it as leftovers with our pork.  Anyway, here's what to do:

2 Granny Smith apples
1 celery root, peeled and cored
1/4 c cider vinegar
salt
1 shallot, minced
2 T whole grain garlic mustard
1/2 c olive oil
2 T chopped fresh tarragon
1 c baby spinach

Slice the apples and celery root into thin match sticks.  Toss with the vinegar and a large pinch of salt.  Mix together the shallot and a large pinch of salt in a small bowl.  Whisk in the mustard, olive oil, and tarragon.  Pour the dressing over the apple mixture and toss to combine.  Let the mixture sit for about 20 minutes.  When ready to serve, add in the spinach.